setting the security repo from buster to testing. So we don't have to keep changing them every time for newer releases

- The Calamares Installer now follows the Hamara style guide for the
colours on the sidebar

- Added a line to extended description

- changed the compat level and decription as per debian policy

also this package has no docs to install as done by that option

- changed the description to satisfy lintian

only till we get new backgrounds.